oc中在image view的view中添加一个textfield，textfield不能编辑？

UIImageView *person = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"geren"]];
 person.frame = CGRectMake(10, 10, 300, 130);
 UITextField *newPwd = [[UITextField alloc] initWithFrame:CGRectMake(95, 55, 185, 21)];
 newPwd.borderStyle = UITextBorderStyleRoundedRect;
 newPwd.autocorrectionType = UITextAutocorrectionTypeYes;
 newPwd.placeholder = @"输入您的新密码";
 newPwd.secureTextEntry = YES;
 newPwd.returnKeyType = UIReturnKeyDone;
 newPwd.clearButtonMode = UITextFieldViewModeWhileEditing;
 [newPwd setBackgroundColor:[UIColor whiteColor]];
 [person addSubview:newPwd];